Photometer.



-0."H SHARP & P. s. MILLAR PHOTOMETER.

APPLIOATION IILED DEC. 26, 1907.

s SHEETS-SHEET 1.

Patented June '7,

G. H. SHARP & P. S. MILLAB.

PHOTOMETER.

APPLICATION FILED DEG. 26, 1907.

Patented June 7, 1910.

3 SHEETS-SHEET 2.

0. H. SHARP & P. S. MILLAR. PHOTOMETER.

APPLICATION FILED D30. 26, 1907. v 96Q,42Q, Patented June 7,1910.

3 SHEETS-SHEET 3.

Q i hm FIE-[5 AT ORNEY CLAYTON H. SHARP, OF WHITE PLAINS, AND PRESTON S. MILLAR, OF BROOKLYN,

' NEW YORK.

PHOTOMETER.

Specifications)! Letters Patent.

Patented June V, 19 10.

Application filed December 26, 1907. Serial Ho. 408,070.

United States gf America, and residents of,

respectively, WVhite Plains, 'in the "county of 'Westchester and State of New York, and

Brooklyn, in the county of Kings and State of New York, have invented .certain new and useful Improvements in Photometers, of which the following is a specification.

Our invention, which relates to an apparatus for measuring candle-power and general illumination, has, for its aim, to provide an improved portable photometer,

which is both simple and accurate in con:

struction and operation; and which has a wide range or scope so that it may be used in any of the eat variety of measurements and degrees of illumination that may be encountered in practice.

The objects of the invention are, further, to provide means for eliminating or minimizing the sources of error which too often exist in photometers; and to put on the market, an instrument which may be sold at a. reasonable price.

Our hotometer is so invented as to secure a sufiicient degree of precision without complication of construction, without a; prohibitive cost, and without involving delicate arts which would easily get out oforder y rough handling.

Our portable photometer is applicable to a sufficiently precise measurement of the candle power 4' of incandescent electric or other lamps, either in a dark or light room; to the determination of the intensity of the total illumination intensity produced at a given point by any number of sources of light, with the desired accuracy; to the measurement of the candle-power of street lamps, or of the general illumination produced thereby; and to the measurement oi" a shutter, permitting the scale to be illumir,

nated by the'lamp in the carriage, andread from the exterior of the box; and-a translucent test plate which may be readily ad.- justed at any desired angle, and which may be used for measuring either candle-power or illumination intenslty. When measuring candle-power, this plate is a difi'using test plate, protected from all but the direct rays of light from the light source tested, by the tube or box in which it is'located. When measuring illumination intensity, the. lower surface which is illuminated by transmitted. light, is viewed through reflecting devices.

The invention also involves absorptionscreens which may be laced on either side of the photometricevice, whereby the range of intensities measurable, is greatly increased.

We will now describe in detail'what is exhibited in the drawings, without any regard to novel or old points.

' Figure 1 is a perspective elevation of the general organization, with the lid of the box open. Fig. 1 is a cross-section of Fig.1, just to the left of the lamp carrier 5. Fig. l is a similar, fragmentary View "showing the shutter 26 open. Fig. 2 is a side elevation of the photometer, with portions of the sides broken away to exhibit some of the interior construction. Fig. 3 an en.- larged sectional View of the reversible reflector seen also at the left hand .end of F ig. 2. Fig. 4 is an opaque cap. Fig.5 is a plan of the whole photometer, with the lid open, and with one or. two details broken away. Dotted lines indicate some of the hidden parts. F'g. 6 is a plan of a portion of the case, to show es eclally, the shutter for the photometer. Fig. 7 is an elevation of one of the apertured opaque screens by itself. Fig. 8 shows, in section, aportien of such a screen to indicate the attachment 0f the propelling cord. The scale of the drawing is enlarged. Fig. -9. is aplan of the compartment containing the prisms, and some other elements not readilyseen in the other figures. Fig. 10 is aplan diagram to indicate .the nature of the device for forming concentric illuminated areas. Fig. 11 a side view of the prisms. Fig. 12 is an end elevation of the photometer with the end of the box omitted. Fig. 13 is an end elevation of the photometer. Fig. 14 is an inverted plan of the reducing screens.

' The containing box is represented by the numeral 1, while 2 indicates apartition for forming a compartment at one end. I

3 indicates the -cover, attached to the case by hinges 4.

The box may be used horizontal or at any angle desired.

5 is the movable comparison lamp carrier, for the lamp 5*, having a base 6, with forked lugs 7, whichare movable along guide rails 8, from about one end of the case, toward the partition 2, for the usual purpose of varying the distance of the source of the comparison li ht from the test plate. In order to pro e the lamp carrier 5 from the outside of t e box 1, there is provided a wheel handle 9 on the outside, connected to a pulley 10, on the inside of-the case. One end of a cord .11 is attached to a forward end pole 12 of the carrier 5, then passes partly around pulleys at 13, then once around the pulley 10, then partly around pulleys 14 and then is fastened to the rear end of the carrier 5.

In conjunction with the above elements, is a plurality ofapertured screens 15, 15*,

15, of opa ue material, one square aperture 16 bein fu ly seen, in Fig. 7 of the drawlrigs, hen the carrier is propelled, it

pushes, first the screen 15, then it and the screen 15, and then all three screens'toward the partition 2. I When the carrier, 5 recedes, the cords 17, connecting the screens 15, 15, 15?, together, and to the carrier 5,-space the screens at intervals along the case.

18 represents holes through which the cords 17 pass for attachment to the screens. The screens 15, 15 15 ride on rods 19, which pass loosely through holes 20. The function of the a ertured screens .15, 15",

and 15 is to cut 0 from' the final aperture 21, inrthe partition2, all the light which is not absorbed bythe black interior surfaces of the case 1 and 'lid' 3. Only the direct rays of light from the movable lamp, find their way to the aperture 21. The cords'17, are supported, not. only bythe screens 15, 15, 15, but alto by rin 22 sliding on the rods 19. The left han ends of the cords 17 are fastened to the partition 2. ,Obviously, the screens .15, 15 15, should 'be black to actas light absorbers.

The carrier 5 is provided laterally with an aperture 23, and a pointer 24, opposite said aperture23, and located between said'aperture 23 and a slot .in.,the side of the box 1, covered by a glass plate 25, which may have a graduated scale as indicated in Fig. 1, for indicating the luminosity of any object. Within the box land along the slot,behind the scale, is a shutter 26, carried on a shaft 27, which have their bearings retspectively in the right hand end 1, of the case 1, and the projecting bearing 28 on the inside of the case 1, nearthe partition 2, said shutter reaching the whole length of the translucent scale. v

29 is a rotary handle for the shutter, on' the outside of the box 1. When the shutter is opened a little, the scale on the glass 25 is illuminated by the movable lamp at that portion where the pointer 24 may to be. The shutter does not open happen very wide illumine the pointer 24.

'\ ---Opposite the external light receiving tube 31, a-ndlocated within the compartment, behind the partition 2, is a prism 32; and oppobut sufficiently to let enough light site the standard lamp and telescopic eye tube 3O, is a prism 33.. The prism 32 has a receiving plane surface'34 for the incident rays of lig surface being perpendicular to the rays, and a total. reflecting surface 35, for directing the rays at right angles to their former direction; while the prism 33 has a receiving 'plane surface 36, perpendicular to the rays from the standard lamp, a plane annular surface 38, perpendicular to the surface 36 while both prisms have plane surfaces at 39,

in contact with each other, which are indicated in the face views of the prisms as the circular area 42.

The nature may be understood further, by describing the action. An external light ray 43, passes through the prism 32, is totally reflected at the surface 35, and passes through the surfaces of. contact within the circular area 42, to the eye tube 30. A ray 44 from the movable'lamp, also passes directly throughthe contact surfaces within the circle 42, but some other ray, as 45, is totally reflected from the annular surface 41, to the eye tube 30. Thus'the observer at the eye tube 30, will see two concentric areas. The lamp holder 5, is therefore moved until the two areas are equally luminous. The external light might-be too bright, or. the comparison light might be too bright for securing equal luminosity. There are provided, therefore, absorbing screens 46 tube 31. As the screens 46 and 47 are invisible to the operator, there is "a scale 51, on the cover 52, which is over the screens 46 and 47 and also there is anindex finger 53 extendin from the disk 50, for indicating the positions of the hidden screens. To hold ht from without the box 1, said total reflecting surface 37, and another plane the screens in the positions desired, is a pin 54 on'the arm 48, pressed by a spring 49 for pushing the pin into counter-sinks 55.

' graduated accordingly.

scale will befrom 0.2 to 0.004, or with the other screen, the range will be 0.04 to 2.

The details of the receiving tube 31 will now be described. It is an elbow, with one arm inserted into a hole in the left hand end of the box 1. At-the outer, or external light receivingend, is a diffusing glass 56, which however is removable, being on a cap 57. Evidently, this cap 57 may be removed, and an opaquecap aplied as a cover, when the instrument is shipped. At the turn of the tube 31, is a reversible reflector, v58, one end havingamirror, 59, .andthe other end carrying a diffusing reflector, =60. Screw threads 61 and 62 permit the reversible reflector to be inserted, either with the mirror or d-iffusin reflector at half a rightangle to the di using medium 56, and to the prism 32. v

63' is an opaque cap' to be screwed upon either the screw 61 or 62.

The elements 56 and 59 areused together; the diffusing reflecting plate 60 is used alone with the medium 56 removed, for candle power measurements.

64 is a diffusing plate at the opening 21 in the partition 21 It is removable. p

65 is a rheostat for regulating the current of the movable lamp.

The elbow tube 31, which is rotary, being held by friction, carries a pointer 31, opposite a scale 31, on the end of the case 1, as in some instances it is an advantage to measure the angle at which a particular iaxternal source of light stands to a vertical me. Y

Themodus opemmli of this photometer will now be set forth in full. I

Assume that it is desired to measure the candle-power of a source of li ht. The diffusing screen 56 is removed from the tube 31, and the diflusin reflector 60 is turned toward the inside 0 the receivin tube 31. Then a suitable standard of light 1s set at a known distance from the diffusing reflector 60, in the prolongation of the axis of the portion of the tubev 31, which is at right angles to the photometer box. Having set up this standard of light, and the current being properly adjusted to a known value on the lamp 5*, the distance of the carriage 5 may be adjusted until an equality of illumination exists as observed through the eyetube 30. When this has been done, the lamp which is to be measured is set up at the same distance from the diffusing reflector, 60, as

the standard lam-p has been; that is, it'replaces the standard lamp in the same position. The photometer is again set for equality of illumination in the field, and the new scale reading is taken. The quotient of the scale reading taken with the unknown lamp,

divided by the scale reading taken with the standard lamp gives the luminous lntensigy of the unknown lamp in terms of the stan ard. For instance, suppose the standard lamp is of 16 c. p., and is set up at such a distance from the photometer that when the photometric balance has been obtained in the photometer, the scale reading is 1.6. Another lamp is then substituted for the standard lamp and the photometric balance gives a scale reading of 3.2. The candle power of the unknown lamp is then.

3.2 RX 16 32 c. p.

It is not necessary that the unknown lzgpp should be at the same distance from the fusing reflector 60, providin its -distance and the. distance of the stan ard lamp are known, for the distance can be taken account.

reversible reflector is turned toward the 'inside of the receiving tube 31. Through this mirror, the difl'usin'gplate 56 becomes visible in the photometer eye-piece 30. The procedure then, is properly as follows: The standard lamp, or other standard of light, is set up at such a distance from the late 56 that the illumination which it pro uces on the difiusing glass 56 is one :unit of illumination, or some multiple or sub-multiple of one. The carriage 5 is then adjust-ed until the pointer 24 reads one on the scale. Having done this, the current through the lamp 5" is raised or lowered until, on viewing the photometric arrangement through the tube 30, an equality of illumination is seen to exist. The standard lamp may next be removed, and the instrument used to measure difiused illumination,

in which work it is direct reading as long as the above procedure is followed. The instruinent may be calibrated before it goes 1 the other hand, the illumination on the glass 56 is so feeble asto be less than that indicated at the lowest point of the scale, one of the' same absorblng screens IB-47 may be turned by the head 50 into a position between the diflusing glass 64 and the photometric prisms. By this means, the light from the comparison lamp 5 is reduced in a known and pro-determined ratio. In this way, the range obtainable by the use of the instrument may be extended from 0.01' of the lowest value on the scale to 100 times the highest value on the scale, these values being approximate. V

We claim asour invention 1. In a photometer, the combination of a containing box, two prisms for constituting a photometric device, a plurality of apertured opaque screens for protecting said hotometric device from any lightreflected om the interior of saidv box, a scale, a lamp, a translucent window in said box, an openable shutter for said window for permitting, when open, said'scale to be illuminated from said lamp, a difiusing test plate,

adjustable to difierent angles, and exposed to all kinds of rays of light to be measured, and an eye tube through which said test plate may be viewed.

2. In a photometer, the combination of a case, a rotary elbow receiving tube thereon,

a reversible reflector at the bend of the tube, carryin a mirror on one end, and a didnsion re ector on the other end, and means by-which said reflector may be attached to said tube. v

3. In a photometer, the combination of a box, a rotary elbow receiving tube thereon, a reversible reflector at'the bend of the tube, carrying a mirror 'on one end, a diflusing reflector on the other end, and means by which said reflector. may be attached to said tube; screw threads constitutin said means.

4. n a photometer, the'combination of an elbow light receiving tube, having a threaded hole at the bend thereof, a thread-' "ed tube, for screwing either end of the same into "said elbow tube, a mirror mounted upon one end of'said tube, and a difiusin reigector mounted upon theother end ofisai tu e.

5. In a hotometer, the combination or an elbow ight receiving tube, having a threaded hole at the bend thereof, a threaded tube for screwing either end of the same into said elbow tube, a mirror mounted upon one'end of said tube, a didusing. reflector mounted upon the other end of said tube,

eeaeao and a removablecap at one end of said elbow tube,

6. In a photometer, the combination of a movable lamp, a rism, a .box having openings for external ight, and light from said lamp; light absorbing screens, adjustable from the outside of said box, to bring either of said screens to reduce.the light from either source, and -toremove said screens from the .paths of said light, and an indicator for noting the positions of said screens.

7. In a photometer, the combination of a movable lamp, a rism, a box having openings for external ight, and light from said lamp, light absorbing screens, adjustable from the outside of sald box, to bring either of said screens to reduce the light from either source, and to remove said screens from the paths of said light, and means for adjusting said screens, consisting of a rotary carrier therefor, a handle for the car-' rier, and a spring I catch for retaining the screens in the positions to which they are adjusted."

8. In a photometer, the combination of a box, a movable lamp holder in said box, a

plurality of spaced and apertured opaque screens standing across the interior of said box, opposite said holder, with the apertures substantially on the same axial line from said holder, and a flexible-connection be'- I tween said holder and said screens.

9.- In a photometer, the combination of a box, a movable lamp holder in said box, a plurality of spaced and apertured opaque screens standing across the interior of said box opposite said holder, with the apertures substantially on'the same axial line from said holder; said screens and holder being movable to and from one another, and a flexible connection between said holder andsaid screens.

10. In a photometer; the combination of a box, a movable lamp holder therein, means on the outside of the box for manually mov ing said holder, said means consistin ,of a handle wheel on the outside of the ox, a

pulley carried by said wheel on the inside of the box, a cord wound around. said pulley,

and having. one end attached to thefidrward end of said holder, and the-other end fastened to the rear end of said holder, other pulleys, said cord passing around said other pulleys for changing the direction of travel of parts of the cord.

11. In a photometer, the combination of a box, a movable lam -holder therein, means on the outside of the ox for'manually moving said holder, said means consisting of a handle wheel on theoutside of the box, a cord wound around said pulley, and havin one end attached to the forward end of sai holder, and the other end fastened to the rear end of said holder, other pulleys, said cord passing around said other pulleys for changing the direction of travel of parts of the cord, a plurality of movable apertured opaque screens located in the path of, and

movable by said holder, guide rods for said screens, easily flexible cords connecting said screens, and sliding rings on said guides and attached to said cords.

12. In a photometer, the combination of a movable lamp holder, movable apertured screens in the path thereof, a box containing said elements, means for moving said holder against the first screen, then said holder and first screen against the second screen, and so on until all the screens have been propelled, and said means being also for moving said holder and screens back again to their first normal positions, a stationary screen 2 having an aperture in line with the apertures in said apertured opaque screens, and a prism on the opposite side of the stationary screen from said opaque screens. 7

13. In a photometer, the combination of a movable comparison lamp holder, movable apertured opaque screens in front thereof, and cords connecting the above named elements together.

14. In a photometer, the combination of a movable comparison lamp holder, apertured opaque screens in front thereof, and cords connecting the above named elements together, a pointer carried by said holder, a scale along the path of said pointer, and a shutter over the scale, said holder having a window for allowin illumination of the scale at the location 0 said pointer.

15. In a photometer, the combination of a movable lamp, a scale for indicating illumination, a box, a shutter inside the box for covering said scale, and a disk handle on the outside of said box, for operating said shutter, and said shutter being for permitting the illumination of certain portions of. .said scale by said movable lamp.

16. In a photometer, the combination of a box, having a longitudinal opening, on the side thereof, a translucent plate with a graduated scale fitted over said openin a lamp carrier, a ointer attached to sai carrier, and locate close to said scale, a shutter arranged over the opening, and means for opening and closing said shutter from the outside of the box.

LEONARD J. LEWINSON. 

